Our long-range objectives are (1) to identify those infants from a clinically normal birth population who will later on become at risk for developmental difficulties, and (2) to identify those infants from at-risk populations who are likely to show normal developmental progress. To meet these objectives we will study a medically normal group of infants and two at-risk groups (prematures and full-term small-for-gestational-age infants). Infants within each of these groups will be assessed for their patterns of sleep-wake states, and respiration recordings will be obtained while the infant is asleep. In addition, the interactions of the mother with her infant will be observed and recorded. These infants will be followed-up through one year of age, and assessed on a variety of developmental measures. We expect to find significant relationships between our early measures of state, respiration, and mother-infant interaction and the later assessment data. In addition to the major human longitudinal program, we will also study an animal model using rabbits. Two at-risk conditions will be generated, one by natural means based upon birth weight (a model for the small-for-gestational-age condition) and the other by the experimental procedure of rearing newborn rabbits in isolation. These animals will have their sleep and wake states measured in a manner similar to the human infants. These animals will be followed through adulthood to determine the long-term consequences of the two at-risk conditions and to determine the nature of the relationships between the early sleep-wake developmental patterns and later behaviors. The findings from the animal studies will then be used as a source of hypotheses for those involved in studying human infants.